Radon contamination in existing buildings is a wide spread problem in many areas of the country. Most prominently, there exists an interstate ridge of uranium material that was deposited over the tri-state area of Connecticut, New Jersey and Pennsylvania during the last ice age. As the uranium decays, it emits radon, a colorless and odorless radioactive gas that easily infiltrates buildings and other dwelling structures. The radioactive radon in turn decays, giving rise to harmful progeny that, when inhaled, can lead to lung cancer and other congestive maladies.
Many buildings in the tri-state area were built upon the existing uranium ridge before cognizance of the problem. As a result, these contaminated buildings presently require radon testing and remediation.
Current technology for preventing radon infiltration into homes and other occupied buildings falls into two categories:
(1) active devices which employ continuously running fans to maintain a reduced air pressure beneath the building, thus preventing the radon from seeping into the building through foundational elements; and PA1 (2) passive systems involving radon-resistant construction that provides a barrier between the home and the source of radon (i.e, the ground beneath the building).
Present radon-resistant construction employs a plastic membrane installed over the concrete slab on which the house is constructed. However, it is general practice to punch holes in the plastic to allow access of air to the concrete as it cures, compromising the integrity of the sheet as a radon barrier. Even a tiny hole will allow radon atoms to pass and contaminate a dwelling.
Even if the integrity of the plastic membrane barrier were maintained, however, this method addresses only present, on-going construction. Generally, the plastic barrier cannot be retrofitted into existing radon-infiltrated buildings. Therefore, exhausting radon gases by continuously running fans is generally the only remediation choice currently available to property owners. This method has many disadvantages, such as: a) the cost of the exhaust fan remediation system is high; b) the exhaust fan remediation system has a limited operative life and must be refurbished periodically; and c) the remediation is not always completely successful due to improper workmanship, installation and materials.
The present invention reflects the discovery that glass fiber mats can replace the plastic barrier sheet. Glass fiber mats can be employed to effectively filter out the natural radioactive gas and its radioactive progeny from soil gases entering a building. Such mats are inherently porous, but current testing has shown that glass fibers in a close-packed geometry are capable of substantially retarding the passage of radon through them, while still allowing air to penetrate freely. Radon has a radioactive halflife of 3.8 days, so that with a sufficient degree of radon retardation, such mats would provide an effective barrier to entry of radioactive radon into a building. It is both possible and desirable to retro-fit existing structures with these mats, thus reducing the costs of present remediation techniques.
Radon gas atoms that are retained in these glass fiber mats will decay in time to other radioactive decay products (RDPs). These progeny comprise electrically charged metal atoms and would be efficiently entrapped by adsorption into the glass fibers.
In addition, the glass fiber mats can be analyzed retroactively for the presence of radon decay products to determine the prior levels of radon entering the building.
There is a present need in the epidemiological study of radon as a health hazard to establish prior levels of radon in the air of dwellings. Current art involves the placement of dosimetric devices for a period of a few weeks to a few months, and their subsequent retrieval and analysis. It is conventionally assumed that such measurements represent the prior radon levels.
Glass fiber mats that are in place in typical housing construction as insulation, as well as newly-installed, radon prevention mats, could be analyzed by existing techniques for the presence of long-lived RDPs of radon, especially lead-210, which has a halflife of about 21 years. The level of such RDPs that are found in the existing insulation of a dwelling, or in the prevention mats, could be used as a measure of the total integrated radon level to which such a dwelling had been subjected.